Image projection system with improved contrast having single birefringence-compensating element

Abstract

The present invention relates to an image projection system ( 1 ) comprising an illumination system ( 3 ) for supplying an illumination beam, a modulation system ( 11 ) for modulating said illumination beam, and an optical system for projecting an image. The modulation system ( 11 ) comprises at least one image display panel of the TN type. The liquid crystal layer ( 13 ) is enclosed between a first polarizer ( 12 ) and a second polarizer ( 14 ). A single birefringence-compensating element ( 27 ) is present between the liquid crystal layer ( 13 ) and one of the polarizers ( 12; 14 ). The element ( 27 ) has a tilted director profile whose projection in the plane of the polarizers encloses an angle 0°<φ≦15° with the active rubbing direction of the liquid crystal layer.

What is claimed is:  
     
       1. An image projection system comprising an illumination system for supplying an illumination beam, a modulation system for modulating said illumination beam in conformity with image information to be projected, and an optical system for projecting an image, said modulation system comprising at least one liquid crystalline image display panel having a first and a second polarizer between which a layer of TN (twisted nematic) liquid crystalline material is enclosed, characterized in that a single birefringence-compensating element is located between the layer of TN (twisted nematic) liquid crystalline material and one of the two polarizers, which element is present on that side of the liquid crystalline material having its active rubbing direction and which element has a tilted optical director profile whose projection in the plane of the polarizers encloses an angle φ having a value 0°<φ≦15° with the active rubbing direction of the layer. 
     
     
       2. An image projection system as claimed in  claim 1 , characterized in that the birefringence-compensating element is an element having a negative birefringence. 
     
     
       3. A head-mounted display comprising a liquid crystalline image display panel, an optical system for imaging an image in an observer's eye, and a head-support, wherein the liquid crystalline display panel is implemented as the image display panel in the image projection system as claimed in  claim 2 . 
     
     
       4. A liquid crystalline image display panel for use in an image projection system, comprising a layer of TN (twisted nematic) liquid crystalline material which is enclosed between a first and a second polarizer, wherein the, liquid crystalline image display panel is implemented as recited in  claim 2 . 
     
     
       5. An image projection system as claimed in  claim 1 , characterized in that the element comprises a negative birefringent foil having a tilted optical director profile. 
     
     
       6. A head-mounted display comprising a liquid crystalline image display panel, an optical system for imaging an image in an observer's eye, and a head-support, wherein the liquid crystalline display panel is implemented as the image display panel in the image projection system as claimed in  claim 5 . 
     
     
       7. A liquid crystalline image display panel for use in an image projection system, comprising a layer of TN (twisted nematic) liquid crystalline material which is enclosed between a first and a second polarizer, wherein the liquid crystalline image display panel is implemented as recited in  claim 5 . 
     
     
       8. A head-mounted display comprising a liquid crystalline image display panel, an optical system for imaging an image in an observer's eye, and head-supporting means, characterized in that the liquid crystalline display panel is implemented as the image display panel in the image projection system as claimed in  claim 1 . 
     
     
       9. A liquid crystalline image display panel for use in an image projection system, comprising a layer of TN (twisted nematic) liquid crystalline material which is enclosed between a first and a second polarizer, characterized in that the liquid crystalline image display panel is implemented as claimed in  claim 1 .